Sound absorbing cementitious tile

ABSTRACT

A die assembly for providing a gypsum ceiling tile having improved acoustic absorption properties includes a punch plate having punches which form perforations through a plasterboard tile and indentors which form indentations in the tile. The punches and indentors are arranged in elongate strips to produce fissure-like perforations and indentations. A stripper plate having apertures corresponding to the punches and indentors and a die plate having apertures corresponding to the punches sandwich the tile, and the punch plate is applied to the tile.

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No., PCT/GB97/00400, which has anInternational filing date of Feb. 10, 1997, which designated the UnitedStates of America, the entire contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cementitious tile having goodacoustic properties, to a method of making such a tile and to a dieassembly for use in the method.

2. Description of the Relevant Art

Board made from gypsum plaster is generically termed plasterboard.Conventional paper faced plasterboard is used as a cladding for buildinginteriors, either to give, or to provide a base for, the desireddecorative finish.

Plasterboard has been successfully used in other applications, such asceiling tiles, but has not generally been very successful inapplications where good acoustic absorption properties are required.GB-A-2 203 772 discloses a plasterboard having relatively good acousticabsorption properties. The board is perforated by holes or slits whichare covered on one face of the board by cloth bonded to the board.WO-A-87/00116 discloses a plasterboard for use as an acoustic tileperforated with regular slots. It has been desired to improve theacoustic absorption properties of plasterboard tiles; it has also beendesired to achieve this in a tile of esthetically pleasing appearance.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a sound absorbenttile comprising cementitious material having through perforations whichextend through cementitious material, characterised in that at leastsome of the perforations are fissure-like perforations. Preferably someof the perforations are circular in section.

By “fissure-like” is meant generally elongate perforations havingirregular edges, preferably with an aspect ratio (the ratio of thelength of the fissure to its maximum width) of at most 4:1. An aspectratio of at least 2:1 is preferred.

Preferably, the tile is lined, for example with a paper liner and thelined surface has an array of indentations which extend through theliner and terminate in the cementitious material. The liner of theplasterboard is ruptured, giving rise to a product of distinctiveappearance. The liner is forced into the indentations during theirformation giving rise to a level of contrast in between the two extremesproduced by the machining operations described previously.

Preferably, the openings of the through perforations on the side of theboard opposite the lined surface (if any) are covered. In an especiallypreferred embodiment, these openings are covered with a sound absorbentmaterial, preferably in sheet form such as acoustic paper or felt.

Also according to the invention there is provided a method ofmanufacturing a sound absorbent tile of cementitious board comprising:

contacting a planar surface of a cementitious board with the profiledsurface of a punch plate having punches thereon, the shapes of at leastsome of the punches being such as to form fissure-like perforations;

perforating the board with fissure-like perforations by applyingpressure between the board and the die such that the punches passthrough the board; and

thereafter separating the punch plate from the board.

Preferably, the profiled surface of the punch plate includes indentorsof similar shape to the punches, shorter than the punches, the methodcomprising embedding the punches and the indentors in the board so thatthe punches through the board and the indentors penetrate but do notpass through the board.

If the board is lined, it is preferred that the punch plate impinges onthe lined surface.

In a preferred method, the planar surface of the board is painted afterthe board has been punched and indented. In this way, any liner forcedinto the indentations can be left unpainted, particularly if the paintis applied with a roller for example. Painting provides a way of varyingthe degree of contrast between the indentations and the rest of theboard.

In an especially preferred method, the surface of the board is spikedusing a roller having radially extending spikes. Spiking can be used toproduce fine pinholes in the surface of the board which gives aparticularly pleasing appearance in combination with the fissure-likeperforations and indentations.

Also according to the invention there is provided a die assembly for usein perforating cementitious board, comprising a punch plate and punchesarranged in an array on the surface of the punch plate, the punches eachhaving a substantially elongate fissure-like profile, to formfissure-like perforations in a board. Preferably, the die assemblyfurther comprises indentors of similar shape to the punches forpenetrating a cementitious board, the inventors being arranged on thesurface of the punch plate and extending a smaller distance from thesaid surface than do the punches. Particularly preferably, the punchplate also carries circular punches for producing circular perforationsin the board in addition to the fissure-like perforations.

It is preferred that the punches extend beyond the indentors by anamount at least as great as the thickness of the cementitious board sothat the punches will have passed through the board before the indentorsimpinge on the board, thus making the through perforations before theindentations. By making the perforations before the indentations, thesize of the press required to put the die assembly into operation iskept to a minimum.

It is also preferred that the die assembly includes a stripper plate anda die plate between which a tile is sandwiched to be perforated. Thestripper plate has holes therethrough to allow the punches andindentors, if any, to pass through the plate and into the tile, and thedie plate has holes therethrough for the parage of the punches afterthey have perforated the tile.

The punches and indentors may be formed of groups of adjacentcylindrical punch pins or by single punches or indentors of the desiredshape. The holes in the punch plate to receive the punch pins or thepunches and indentors can be formed by a wire erosion technique.Alternatively, the punches and indentors may be of a ceramic materialset into a binder on the surface of the punch plate.

Also according to the invention there is provided a suspended ceilingcomprising the tiles of the invention. Such a ceiling can havenon-uniform acoustic properties and a substantially uniform appearanceby using a mixture of tiles according to the invention and tiles ofsimilar appearance having no through perforations but only fissure-likeindentations. Ceilings can thus be made having desired overall acousticproperties; for example a ceiling can be made which is particularlysuitable for an auditorium where speech must be clearly audiblethroughout.

DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described in detail, by wayof example, with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross sectional view of a die assembly accordingto the invention in use to make a tile according to the invention;

FIG. 2 shows a schematic perspective view of the punch plate of FIG. 1;

FIG. 3 shows part of a tile according to the invention; and

FIG. 4 shows graphically the results of acoustic tests in a tileaccording to the invention and a control.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 illustrate part of a die assembly 10 which includes longpunches 12 and indentors 14 attached to a punch plate 16. The punches 12consist of several punch pins 18 and the indentors 14 consist of severalindentor pins 20; the pins 18,20 are rigidly attached to the punch plate16, for example by welding or by having threaded lower portions whichscrew into threaded holes in the plate. The pins 18,20 are arranged ingroups (see FIG. 2) to form punches 12 and indentors 14 which impartfissure-like perforations and indentations to a plasterboard tile 22 towhich the die assembly 10 is applied. The punch pins 18 are cylindricaland are longer than the indentor pins 20. The punch plate preferablycarries also single, circular punch pins (not shown) and may carrycircular indentors (not shown).

The die assembly 10 also includes a top, stripper, plate 24 havingapertures 28,28′ corresponding to and large enough to accommodate thepunches 12 and indentors 14, and a bottom, die, plate 26 havingapertures 30 corresponding to the punches 12. In use, the die assembly10 is mounted in a press and a lined plasterboard tile 22 is sandwichedbetween the rigidly mounted stripper 24 and die 26 plates. As the punchplate 16 is moved towards the tile 22, the punches and then theindentors exert a pressure of about 1.5 MN/m² on the tile 22. Thepunches 12 pass through the apertures 28 in the stripper plate 24 andpress into the plasterboard. The punches 12 force plugs of plasterboardthrough the openings 30 in the die plate 26. In this way, theperforations are formed in the tile 22 before the indentors 14 engagethe tile. As the punch plate 16 continues to advance towards the tile22, the indentors 14 pass through the holes 28′ in the stripper plate 24and are embedded in the tile. Once the paper liner 32 of the tile 22 hasbeen ruptured by the indentors 14, the operation is complete and thepunch plate 16 is withdrawn.

The clearances between the punches 12 and the corresponding holes 30 inthe die plate 26 should be chosen to ensure that the paper backing, ifany, of the plasterboard tile 22 is cut cleanly away where the punchesexit the plasterboard, while allowing the punches to be withdrawn fromthe die plate. If the top face of the tile is lined, for example withpaper, the appearance of the top surface of the tile can be determinedby the clearance between the punches 12 and indentors 14 and the holes28 through the stripper plate 24. A very small clearance will giveperforations and indentations having sharply defined edges while agreater clearance will give perforations and indentations with less welldefined edges, where the fibres of the liner material are visible atthose edges.

The punch 18 and indentor 20 pins are short lengths of metal rod weldedto the metal punch plate 16, with the longitudinal axis of eachapproximately perpendicular to the plate. By arranging the pins 18,20into elongate strings, a die assembly for producing fissure-likeindentations in plasterboard is created. The pins forming the punchesand indentors need not touch each other; small gaps between them can bedesirable since they add to the irregularity of the edges of thefissure-like perforations and indentations made by the punches andindentors.

After being punched and indented, the fissure (or fissure and circularhole) pattern on the tile can be supplemented by a pinhole patternimposed by spiking the surface of the plasterboard using a roller havingspikes mounted radially on its periphery. The spikes in contact with thetile at any given time have a much smaller cross sectional area than thepunches 12 and indentors 14 so the force on the roller required to drivethe spikes into the plasterboard is significantly less than the forcerequired on the punch plate 16 to produce the fissure indentations.

A tile 40 produced by use of the die assembly 10 is shown in FIG. 3. Thetile has fissure-like indentations A and circular perforations B.Preferably the ratio of fissure-like to circular perforations ispreferably within the range 2:1 to 1:2. It has been found thatsatisfactory acoustic properties are achieved, without significant lossof strength, when about 6% of the total area of the principal faces ofthe tile has perforations. An aesthetically pleasing effect is achievedwhen additionally about 6% of the total area of the front face of thetile has indentations which do not pass through the tile.

FIG. 4 shows the result of acoustic tests conducted according to BS EN20354:1993 on a control plasterboard tile and a plasterboard tileaccording to the invention. Both tiles are 9.5 mm thick, are lined onthe back with 0.5 mm thick acoustic paper, have a surface density of 7kg/m² and have perforations over 6% of their principal surfaces. Theperforations in the control tile are 4mm diameter holes at 15 mmcentres; those in the tile according to the invention are fissure-likeperforations.

FIG. 4a shows a plot of the frequency of against the absorptioncoefficient as for the control tile, and FIG. 4b shows the same plot forthe tile according to the invention.

It will be seen from FIG. 4 that the acoustic absorption performance ofthe tile according to the invention is significantly superior to that ofthe control tile over the entire frequency range tested, and that thetile according to the invention exhibits a generally flat acousticprofile, making it well suited to many different acoustic environments.

By varying the proportion of the surface area of the tile taken up byperforations, the acoustic properties of the tiles can be varied. Theappearance of the tiles can be kept constant by providing indentationsinstead of perforations; the indentations have no significant effect onthe acoustic properties of the tile.

One use of tiles according to the invention is in the constructions ofsuspended ceilings. It may be desired to provide an acousticallyabsorbent suspended ceiling having different acoustic properties indifferent parts. Tiles of similar appearance to those of the inventioncan be manufactured having no perforations but only fissure-likeindentations; such tiles can be used with tiles according to theinvention having to provide a suspended ceiling of uniform appearancebut with acoustic properties which vary over the ceiling.

What is claimed is:
 1. A sound absorbent tile comprising: a cementitiousmaterial; and a plurality of through perforations opening on opposingside surfaces of said cementitious material, wherein at least one ofsaid through perforations is an elongate fissure-shaped perforation,having irregular edges and being of constant cross section as saidfissure-shaped perforation passes through said cementitious material. 2.The tile according to claim 1, wherein said cementitious material isgypsum plaster.
 3. The tile according to claim 1, wherein some of saidthrough perforations are generally cylindrical-shaped perforations. 4.The tile according to claim 1, further comprising: a liner coveringportions of said cementitious material.
 5. The tile according to claim4, wherein said liner is formed of paper.
 6. The tile according to claim1, wherein said at least one of said through perforations includes aplurality of elongate fissure-shaped perforations, and wherein saidplurality of fissure-shaped perforations extend in substantially a samedirection.
 7. The tile according to claim 1, further comprising: acovering disposed over an opening of some of said plurality of throughperforations.
 8. The tile according to claim 7, wherein said covering isformed of a sound absorptive material.
 9. The tile according to claim 1,wherein a sum of cross sections of said plurality of throughperforations is approximately 6% of a total cross section of a sidesurface of said cementitious material.
 10. The tile according to claim1, further comprising: a liner covering one side surface of saidcementitious material; and a plurality of indentations extending throughsaid liner and terminating in said cementitious material.
 11. The tileaccording to claim 10, wherein said plurality of indentations arefissure-shaped.
 12. A sound absorbent tile comprising: a generallyplanar member having a generally flat first surface and a generally flatsecond surface, opposite said first surface; and a plurality of firstthrough perforations passing from respective first openings on saidfirst surface to respective second openings on said second surface,wherein each first through perforation of said plurality of firstthrough perforations has a fissure-shaped cross section which continuesin a substantially uniform manner as said first through perforationpasses through said generally planar member from said first opening tosaid second opening.
 13. The tile according to claim 12, wherein saidfissure-shaped cross sections of said plurality of first throughperforations extend substantially in a common direction.
 14. The tileaccording to claim 13, further comprising: a plurality of second throughperforations passing from respective third openings on said firstsurface to respective fourth openings on said second surface, whereineach second through perforation of said plurality of second throughperforations has a circular-shaped cross section which continues in asubstantially uniform manner as said second through perforation passesthrough said generally planar member from said third opening to saidfourth opening.
 15. The tile according to claim 14, wherein a sum ofcross sections of said first openings and said third openings isapproximately 6% of a total cross section of said first surface.
 16. Thetile according to claim 15, wherein said generally planar member isformed of a cementitious material.
 17. A suspended ceiling comprising: aplurality of suspended tiles including a plurality of first tiles, eachof which includes: a cementitious material; and a plurality of throughperforations opening on opposing side surfaces of said cementitiousmaterial, wherein at least one of said through perforations is anelongate fissure-shaped perforation, having irregular edges and being ofconstant cross section as said fissure-shaped perforation passes throughsaid cementitious material.
 18. The suspended ceiling according to claim17, wherein said plurality of suspended tiles exhibits substantiallyuniform acoustic properties and substantially uniform appearance. 19.The suspended ceiling according to claim 17, wherein said plurality ofsuspended tiles further includes a plurality of second tiles, each ofwhich includes: a cementitious material; and a plurality of indentationsin said cementitious material, wherein at least one of said indentationsis an elongate fissure-shaped indentation.
 20. The suspended ceilingaccording to claim 19, wherein said plurality of suspended tilesexhibits non-uniform acoustic properties and substantially uniformappearance.